The present invention generally relates to the field of pressure transducers and more specifically to the field of capacitive pressure transducers.
Capacitive pressure sensors are known and provide a variable capacitance in response to sensed pressure. Examples of such pressure sensors are illustrated in U.S. Pat. Nos. 4,178,621 to Simonelic and Ho, 4,204,244 to Ho and 4,225,632 to Ho, all assigned to the same assignee as the present invention. Typically, such capacitive sensors are utilized by processing circuits to provide an output sensor voltage, typically an analog voltage, which has a magnitude that is directly related to the sensed pressure. One example of such a processing circuit is shown in U.S. Pat. No. 4,250,452 to Gray and Pace and assigned to the same assignee as the present invention. While known processing circuits for pressure sensing devices have performed satisfactorily under most conditions, such processing circuits have not been entirely satisfactory when extremely large ranges of pressures are to be sensed since the output voltage has been found to not vary linearly as a function of sensed pressure over these extremely large ranges of pressure, especially if the magnitude of the output voltage is only permitted to vary over narrow voltage limits. Also, such processing circuits do not generally operate properly over large temperature ranges.
Some prior circuits have utilized an additional pressure variable capacitor, in addition to the main pressure variable capacitor, to attempt to provide a linearized output voltage over large ranges of sensed pressure. Providing such an additional varying capacitor greatly increases the cost of the capacitive sensor element while also complicating the design of the sensor processing circuit.